FI70618B - CHEMICAL MASS WITH FOERBAETTRAD STYRKA AVVATTNINGSBARHET OCH MALBARHET SAMT SAETT ATT FRAMSTAELLA DENNA - Google Patents

Description

7061 8 1 Chemical pulp with improved strength, dryability and grindability and method of making the same The present invention relates to chemical pulps with improved strength, dryability and grindability, and to a process for its preparation. method of making these.

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In the manufacture of lignocellulose-based sheet structures from a suspension of fibers and water, the fibers are first mechanically formed in a wet state.

15 This activity, the grinding activity, is one of the most important unit functions in paper technology. By grinding in different ways, different quality properties of the sheet can be produced and it is possible to change the usability of different fibrous raw materials.

However, the mechanical treatment principles for obtaining different product properties are very vague and, above all, the essential mechanisms of the grinding process are unknown, as a result of which grinding can be said to take place more or less in accordance with the old tradition.

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The fibrous material has a complex morphological structure and the changes that occur in the milling region are heterogeneous in nature, making it difficult to explain them further. Usually the effect of grinding is divided as follows: 30 - shortening of fiber length - production of fine material - cleavage - external fibrillation 35 - swelling - dislocations - reduction of degree of polymerization 7061 8 l.

1 These wet grinding effects in the wet state increase the tensile strength of the fibers, while the coefficient of elasticity of the moon decreases. Ground dried fibers have higher values of both tensile strength and modulus of elasticity than unmilled fibers.

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The properties of the paper are changed most strongly in the early stages of grinding. Usually, increases in density, elongation at break, and all strength properties except tear strength are obtained, while opacity, air permeability, and moisture resistance of the dimensions decrease.

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The analysis of the causes and effects of the effect of grinding on the finished sheet is complicated by the lack of knowledge about how the properties of the paper are created. In general, it can be said that the fine material formed and the softening of the fibers (which means increased expansion) are very significant.

The swelling of the cellulosic fibers can be viewed from the perspective of the physical chemistry of the gels. This shows how various parameters such as pH, temperature, salinity, etc., 20 affect the expansion of the fibers as well as the level of expansion of the fine fiber fractions.

The traditional way to increase efficiency in grinding operations is to change the structure of the grinding members and the concentration of cellulosic material in the grinding device. Further attempts have also been made to change the temperature and pH as well as to add various chemicals to achieve the desired increase in efficiency in the milling process in connection with the papermaking process, i. first in the further processing of the dried pulp.

30 No clear results have been obtained from the mechanical modification of the grinding members. However, a development can be seen in terms of better strength properties of the ground lignocellulosic material after treatment in the grinding equipment now in use. However, with respect to changes in chemical conditions in the milling operation, no major effects have been observed compared to those obtained in conventional papermaking.

It is an object of the present invention to provide a chemical pulp having improved strength, dryability and grindability.

Another object of the invention is to provide a method for producing a chemical pulp having improved strength, dryability and grindability.

These and other tasks are solved by mixing the wood raw material with an aqueous solution of one or more low molecular weight salts after cooking. Preferably 0.1 to 10% by weight of salt, based on the dry mass, is combined.

The essential idea of the invention is that the small molecule salt should be present in the drying, at least in its initial stage.

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It is known that in the drying of the pulp the swollen fiber "sinks", i. the gel structure disappears. Upon subsequent addition of water in papermaking, the fiber does not return to its original state, i. this process is at least partially irreversible. The explanation for the swollen fiber 20 "sinking" during drying is that when the water is removed, the cellulose chains come so close together that hydrogen bonds are formed between them. As a result, the cavities in the gel structure of the pulp disappear. When water is then added during further processing of the pulp, the water is unable to break the hydrogen bonds and an irreversible "depression" is thus formed.

It has now surprisingly been shown that the addition of water-soluble, low-molecular-weight salts to the pulp already after preparation, but before drying, can interfere with the formation of hydrogen bonds. These salts penetrate the cavities of the gel structure and form steric barriers therein, so that the cellulose chains cannot approach each other, thereby largely preventing the formation of hydrogen bonds.

35 By largely preventing the irreversible "depressions" in the gel structure of the fibers, the fibers can swell again with the addition of water and for the most part regain the state they were in before drying.

7061 8 1 This results in improved strength, adhesion and grindability of the treated pulp compared to the untreated pulp.

In carrying out the process according to the invention, the undried chemical, bleached or unbleached pulp is mixed with an aqueous solution of suitable low molecular weight salts. After this addition, the pulp is dried in a conventional manner, e.g. by using flake drying, by supplying heat by radiation or convection (e.g. pulp centrifugal drying) or by heated surfaces possibly subjected to pressure (e.g. pulp cylinder drying).

Suitable salts to be added to the pulp are small molecule, water-soluble salts. It is important that the molecular size of the salts be small enough for them to penetrate the gel structure and settle therein, thereby forming a steric hindrance.

It is further important that the added salt does not form ions that are harmful in subsequent use of the pulp. When the pulp, after drying, is resuspended in water, much of these settled salts are redissolved. Thus, a salt that forms chlorine ions is not always suitable because chlorine ions are often undesirable in subsequent processing. Since the end use of the pulp is often not known to the pulp manufacturer, it is appropriate to use a salt that is used in other contexts in pulp and paper production. Examples of suitable salts include sodium salt and sodium thiosulfate, which are chemicals commonly used in the pulp industry. Organic salts can also be used, provided that they contain molecules small enough to penetrate the cavities of the gel structure.

Very small amounts of active ingredient are required to produce the desired effects. A few or a few tenths of a percent, based on the dry weight of the pulp, is usually sufficient, but can be used up to about 10% by weight.

35 An alternative way of obtaining the desired properties of the pulp is to mix the untreated pulp with the pulp treated as described above in 57061 8 1 in suitable proportions, so that the entire pulp mixture has the desired properties.

The following are examples of embodiments of the present invention, which should not be construed as limiting the scope of the invention as set forth in the appended claims.

Examples 10 The experiments described in the examples have been performed according to the SCAN test methods presented and recommended by the central laboratories of the pulp, paper and wood pulp industries in Denmark, Finland, Norway and Sweden. The following SCAN methods were used: 15 SCAN: C 19: Pulp drying resistance according to the Schopper-Riegler method SCAN: C 24: Pulp milling in a PFI mill SCAN: C 25: Laboratory milling in a Valley Dutchman SCAN: C 26: Preparation of a laboratory sheet for physical 20 testing SCAN: C 27R: Light scattering coefficient SCAN: C 28: Determination of physical properties of laboratory sheets SCAN: C 24: Puncture resistance 25 SCAN: C 11: Tear strength of paper and board SCAN: P 16: Tensile strength and elongation

Example 1 Sodium sulfate (NaSO) was dissolved in water to a suitable concentration, in which solution an undried, bleached softwood sulfate pulp with an initial water content of about 80% was dispersed in a final 5% pulp concept. After a few minutes, the pulp was dried by filtration and compressed to a dry content of about 35%. After air-drying at 60 ° C, the pulp was ground in a Valley Hollander. Here, the pH was adjusted to 5 by decomposition with NaOH or H 2 O. The concentration of sodium sulfate in the dried pulp was calculated from the starting pulp 7061 8

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^ dispersion sec ;; the concentrated mass of the compressed pulp was taken orally. A control cloth was used, which was dispersed in water without the addition of salt and otherwise treated in the same manner as above.

5 The following comparative values were obtained between the comparison and the experiments with different sodium sulphate concentrations:

Tensile index, kNm / kg __ ^ ayhattime_min____ 10 20 30 10 Vert 61 83 92.5

Experiment with 3% NaSO 72.5 92 100.5

Experiment 61 "74.5 94.5 102.5 _10% __ ^ _______________________ L_Z ^ i.2 ______ 15 Example 2

The procedure of Example 1 was repeated, but the drying temperature was 90-95 ° C and sodium sulfate was 5% in the dried experiment. The following results were obtained: 20 ______________________________________________

Tensile index, kNm / kg __Milling time min____ 10 20 30

Translation 58 79.5 89

Experiment ___________________________________ 67 _______ 89 ^ 5 ___ 99.5 25

Example 3

The procedure of Example 1 was repeated, but grinding was performed in a PFI mill and the dried pulp had the sodium sulfate concentrations shown in the table.

The results were obtained by comparison in a similar drying, 30SR: 35 7061 8 7 1 Νβ, ΚΟ., 1 2 4 _______________________________O______3______6______110____

Jauliatnskie.rros, amount 40 () 0 4200 3800 3300 5 _Ve ^ oi nde kai Λ_ ^ Ν'ηι / ^} £ __________ 94 3_00_ 105____107

The results obtained in the comparison with the same tensile index, 85 kNm / kg:

Na2SO4,% 1Q —------ _______________________________________3_______6_______10___

Grinding cycle, amount ________ 3200 2400 2000 1700

Example 4 15

The procedure of Example 1 was repeated, but the pulp was made from undried unbleached softwood pulp. The concentration of sodium sulphate in the dried pulp is shown in the table. The following results were obtained: 20 -

Tensile index, kNm / kg __Milling time min_______________ ____10______20_____30

Vert 39 59 70.5

Experience 0.5% NaSO 44.5 64.5 77.0 25 ___ Κοθ_2λ5% __ ^ _______________________ 47 _____ 66 ± 5 ____ 79.5

Example 5

The procedure of Example 1 was repeated, but the salt was sodium chloride. The following results were obtained:

Tensile index, kNm / kg

Grinding time min _________________10_____20_____30_

Vert 61 83.5 92.5 35 ___Test 5% NaCl ____________________ 72L ___ 89_, 5__102.0 7061 8

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1 Example_6

The procedure of Example 1 was repeated, but the salt was sodium thiosulfate. The following results were obtained: 5 - __ Tensile index, kNm / kg__

Grinding time min__ ______ _ 10_ _20______30__

Value 59.0 82.5 92.5

Test 3% NaSO 67.0 89.5 97.0 10 __Test_6% ____ »___________________________ 74.0 ____ 95 ^ 5__106.5

Example 7

The procedure of Example 1 was repeated, but the pulp was prepared from 15 non-dried unbleached sulphate pulp to which sodium thiosulphate had been added. The following results were obtained: __Traction index, kNm / kg_ ___Milling start min_______________ ____10_____20_______30___ 20 Ver 36.5 56.0 69.0

Experiment 1% NaSO 42.5 62.5 77.0

Experiment 2.5% __ "_______________________ 47 ^ 0 ____ 66.0 ____ 81.5

Example 8 25

The procedure of Example 1 was repeated, but monoethanolamine (MEA), diethanolamine (DEA) or, respectively, triethanolamine (TEA) was added. The following results were obtained: 30 _ Tensile index, kNm / kg __Milling time min .___________________ 10_____20_______30__

Value 57.5 80.0 92.0

Experiment 3% MEA 69.0 90.0 100.5

Test 3% DEA 70.0 89.5 98.5 35 __Test 1.5% TEA __________________________ 84.0 ___ 98.5 7061 8 <)

The procedure of Example 1 was repeated, but the pulp consisted of unbleached sulphate pulp and the additive was urea. The following 5 results were obtained:

Tensile index kNrn / wed _ _Grading start min ^ ________________ 10___20_____30_

Ver. 36.5 56.0 69.0 10 _ Experiment 2.5% urea_________ ____ 42.5 62z5_ 78.5

Example 10

The procedure of Example 1 was repeated with the difference that the starting material here was a dried bleached sulphate pulp. No significant differences between the control and NaSOrn 3, 6 or resp. Between the 10% increase could not be found.

Example 11 20

The unseeded, unbleached bleached sulphate pulp was dried in a conventional manner on a paper machine on a test scale. In this case, a chemical solution (see table) was sprayed onto the wet web before the pressing section. The final amount of additive chemicals in the dried pulp was estimated by extraction with warm water. For ammonium carbonate, which gasifies on drying of the pulp, the added amount was calculated from the concentration and flow of other chemicals above the spray tube. The pulp thus dried was dispersed in a disperser and ground, after which the paper was prepared on an experimental scale, all in a known manner. In papermaking, only chemicals were added to adjust the pH to 6 (NaOH or HSO, respectively). This pH adjustment was already performed in the disperser. The results are shown in the table below. To minimize the effect of variation in longitudinal / transverse strengths, Table 35 shows the tensile strength plate x tensile strength transverse · All strengths were evaluated in the same grinding batch. For comparison, a pulp which had been sprayed with water during drying but which otherwise received the same treatment was used.

Test Tensile index, kNm / kg

Value 63.0 5 0.7% (NH.) SO 68.5 4 2 1.0% (NH,) CO 68.0 4 2 1.0% Na2SO2 68.5 2.0% Na „SO, 73.0 2 4 10 15 20 25 30 35

Claims (4)

A chemical pulp with improved strength, dryness and grindability, characterized in that it contains, as an essential barrier to the formation of hydrogen bonds, one or more small-molecule, water-soluble salts which are incorporated into the pulp after cooking before drying. 1 Claims 1 I 7061 8 Pulp according to Claim 1, characterized in that 10 salts are present in an amount of 0.1 to 10% by weight, based on the dry weight of the pulp. 3. A process for preparing a chemical pulp with improved strength, drying ability and grindability, characterized in that an ethereal barrier to the formation of hydrogen bonds is provided by mixing the pulp with an aqueous solution of one or more small molecular salts after cooking before drying. Process according to Claim 3, characterized in that the salts are added in an amount of 0.1 to 10% by weight, based on the dry weight of the pulp. 20 25 30 35